Temperature control system

ABSTRACT

A temperature control system, including a closed refrigerant circuit having an evaporator unit for absorbing heat via the refrigerant, thereby evaporating it, a compressor unit with a mechanical compressor for increasing the pressure of the refrigerant and a thermal collector for using an external heat source to increase the temperature of refrigerant within the circuit, and a condenser unit for rejecting heat from the refrigerant, liquefying it.

This is a National Phase Application filed under 35 U.S.C. § 371 as anational stage of PCT/IL2010/000863, filed on Oct. 20, 2010, anapplication claiming the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Application No. 61/253,573, filed on Oct. 21, 2009, thecontent of each of which is hereby incorporated by reference in theirentirety.

FIELD OF THE INVENTION

This invention relates to air-conditioning systems, and in particular tothose which provide cooling and/or heating by compressing a workingfluid such as a refrigerant.

BACKGROUND OF THE INVENTION

Air-conditioning systems are commonly provided to provide heating andcooling to a space. A compressor unit is provided to compress andthereby heat refrigerant which is provided thereto in a gaseous state.The compressed a heated refrigerant is passed through condenser coils,where air is forced over them to release heat into the atmosphere,thereby condensing the refrigerant to liquid form. The liquidrefrigerant may pass through a metering device, which regulates the flowof refrigerant while lowering its pressure, then entering an evaporator,which is located in or near a space to be cooled. Air from the space isforced over evaporator coils, which causes heat from the space to beabsorbed by the refrigerant, which becomes a gas. The gaseousrefrigerant is then carried to the compressor unit, where the cyclestarts again.

To provide heating, the direction of flow is reversed. A reversing valveis provided in order to ensure that the direction of flow through thecompressor unit remains the same as when cooling.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided atemperature control system comprising a closed refrigerant circuithaving:

-   -   an evaporator unit configured for absorbing heat via the        refrigerant, thereby evaporating it;    -   a compressor unit configured for increasing the pressure and        temperature of refrigerant within the circuit; an    -   a condenser unit configured for rejecting heat from the        refrigerant, thereby liquefying it;        the compressor unit comprising a mechanical compressor        configured for increasing the pressure of the refrigerant and a        thermal collector configured for utilizing an external heat        source to increase the temperature of the refrigerant.

The thermal collector may comprise a solar collector configured forcapturing heat from incident solar radiation.

The solar-sensitive modules may comprise a photovoltaic cell.

The thermal collector may be arranged downstream of the mechanicalcompressor.

A second thermal collector may be provided, arranged upstream of themechanical compressor.

Each of the thermal collectors may be provided with a bypass configuredto allow the refrigerant to bypass it.

The temperature control system may further comprise a controllerconfigured to control the operation of the mechanical compressor atleast based on an expected temperature increase of the refrigerant inthe thermal collector.

The compressor unit may comprise a variable-frequency drive to vary thespeed of the mechanical compressor.

The controller may be configured to control the operation of themechanical compressor at least by causing the variable-frequency driveto vary the speed of the mechanical compressor.

The temperature control system may further comprise temperature sensorsdisposed so as to measure the temperature of the refrigerant uponentering and exiting the thermal collector, the controller beingconfigured to determine the expected temperature increase based on thetemperature measured by the temperature sensors.

The temperature control system may further comprise one or moresolar-sensitive modules configured to measure the degree of solarradiation available to the solar collector, the controller beingconfigured to determine the expected temperature increase based on thedegree of solar radiation measured by the solar-sensitive modules.

The solar collector may comprise a refrigerant-carrying conduit withinan enclosure, which may be evacuated, a radiation-facing side of theenclosure comprising a transparent material.

The refrigerant-carrying conduit may constitute a portion of a fin-tubearrangement.

The solar collector may further comprise a heat-sink associated with therefrigerant-carrying conduit, the heat-sink being configured to absorbsolar energy and transfer it to the refrigerant-carrying conduit. Theheat-sink may be formed with at least a portion of therefrigerant-carrying conduit, and/or it may be formed so as to receiveat least a portion of the refrigerant-carrying conduit therewithin.

The heat-sink may be formed with projections extending radially from therefrigerant-carrying conduit. The projections may extend along a portionof the refrigerant-carrying conduit.

The heat-sink may be made of an extruded material.

The heat-sink may be made of a metal.

At least radiation-facing surfaces of the heat-sink may be designed tolower reflectivity thereof.

The temperature control system may be configured to operate avapor-configuration refrigeration cycle.

The temperature control system may further comprise a metering device,such as a thermostatic expansion valve, downstream of the condenser unitconfigured for regulating the flow of liquid refrigerant.

The temperature control system may be a split-system air conditioningsystem.

The temperature control system may further comprise a reversing valveconfigured to cause the refrigerant to flow in a reverse direction,thereby enabling the evaporator unit to reject heat from therefrigerant, and the condenser unit to absorb heat to the refrigerant,i.e., to cause heat to be absorbed thereby.

The condenser unit may constitute a portion of a water heating system,the water heater being configured to utilize the heat rejected from therefrigerant to heat water. At least a portion of the condenser myconstitute part of a heat exchanger in order to enable the heating ofthe water.

According to another aspect of the present invention, there is provideda reversing valve comprising first and second supply connections, andinlet, an outlet, and first and second valves; the reversing valve beingarranged such that the first and second valves are configured toselectively:

-   -   bring the first supply connection in fluid communication with        the inlet and fluid isolation from the outlet, and the second        supply connection in fluid isolation from the inlet and fluid        communication with the outlet; or    -   bring the second supply connection in fluid communication with        the inlet and fluid isolation from the outlet, and the first        supply connection in fluid isolation from the inlet and fluid        communication with the outlet.

The first and second valves may be three three-way valves, eachcomprising first, second, and third ports, and being configured suchthat the second port may be brought into fluid communication with onlyone of the first and third ports.

The valves may be connected such that:

-   -   first ports of each valve are in fluid communication with each        other and with the first supply connection;    -   third ports of each valve are in fluid communication with each        other and with the second supply connection;    -   the second port of the first valve is in fluid communication        with the inlet; and    -   the second port of the second valve is in fluid communication        with the outlet.

The valves may be mechanically coupled to one another such that theyalter their states of fluid connectivity in tandem with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, embodiments will now be described, by way ofnon-limiting examples only, with reference to the accompanying drawings,in which:

FIG. 1 is a schematic illustration of an air-conditioning systemaccording to the present invention;

FIG. 2 is a perspective view of a solar collector for use with theair-conditioning system illustrated in FIG. 1;

FIG. 3 is a schematic illustration of another example of anair-conditioning system according to the present invention;

FIG. 4A is a schematic illustration of a reversing valve for use withthe air-conditioning system illustrated in FIG. 3;

FIGS. 4B and 4C schematically illustrates operation of the reversingvalve illustrated in FIG. 4A, in cooling and heating modes of operation,respectively;

FIG. 5 is a schematic illustration of a further example of anair-conditioning system according to the present invention;

FIG. 6 is a schematic illustration of a modification of a condenser unitof the air-conditioning of the present invention;

FIG. 7A illustrates a heat-sink for use with the solar collectorillustrated in FIG. 2; and

FIG. 7B is a cross-sectional view taken along line V-V in FIG. 7A.

DETAILED DESCRIPTION OF EMBODIMENTS

As illustrated in FIG. 1, there is provided an air-conditioning system,constituting a temperature control system, which is generally indicatedat 10. The system 10 comprises an evaporator unit 12, and compressorunit 14, a condenser unit 16, and a metering device 18. The system 10further comprises a refrigerant line 20, which is configured to carryrefrigerant among the above-listed components of the system 10. Theair-conditioning system 10 is configured to operate avapor-configuration refrigeration cycle in order to provide cooling viathe evaporator unit 12.

The evaporator unit 12 may be designed similar to evaporator units whichare typically provided for use in air-conditioning systems. As such, itcomprises an evaporator coil 22, disposed so as to be in fluidcommunication with the refrigerant line 20, and a fan 24, or othersimilar forced air mechanism, designed to force ambient air of the spaceto be cooled over the evaporator coil. The evaporator unit 12 isdesigned such that refrigerant which enters the evaporator coil 22 at anentrance 26 thereof in a liquid state exits the evaporator coil at anexit 28 thereof in a gaseous state.

The compressor unit 14 is disposed downstream of the evaporator unit 12,such that it receives refrigerant in a gaseous state therefrom, and isdesigned such that refrigerant which enters at an entrance 36 thereof ina gaseous state exits at an exit 38 thereof in a gaseous state at ahigher pressure and temperature. It comprises a mechanical compressor30, which may be which may be designed similar to mechanical compressorstypically provided for use in air-conditioning systems, and a solarcollector 32 connected thereto. The mechanical compressor 30 and solarcollector 32 are arranged such that refrigerant enters the solarcollector after it has passed through the mechanical compressor. Thecompressor unit 14 further comprises a controller 40, configured tocontrol the operation thereof, as will be explained below.

The mechanical compressor 30 is configured to raise the pressure, andthus the temperature, of the gaseous refrigerant. It is provided with amotor 34 to drive its operation. The motor 34 may include avariable-frequency drive, which is designed to vary the speed of themotor 34, such that the compressor may work at a partial load, forexample in response to a decreased cooling demand. Such an arrangementmay be sold under the “Inverter” tag.

The solar collector 32 comprises a solar coil 42 constituting arefrigerant-carrying conduit, designed to be in fluid communication withand receive compressed refrigerant from the mechanical compressor 30.The solar coil 42 is provided so as to be exposed to solar radiation,thereby increasing the temperature of the gaseous refrigerant. The solarcollector 32 may further comprise any arrangement to increase theefficiency thereof, including, but not limited to, solar reflectors,vacuum tubes surrounding the solar coil 42, a fin-tube arrangement, etc.

As illustrated in FIG. 2, the solar collector 32 further comprises anenclosure 44 containing the solar coil 42 therewithin. The enclosure 44comprises a radiation-facing side 46, which is designed for facing thesun when the system 10 is installed, and which is designed to allow themaximum amount of solar radiation, or the maximum amount ofpredetermined frequencies of solar radiation (for example infrared), topass therethrough. The enclosure 44 may be evacuated, i.e., once thesolar coil 42 and any other solid components are installed therein, avacuum may be produced in the remaining space, or filled with an inertgas, or any other transparent insulating substance. This reduces heatloss from the solar coil 42 to the atmosphere surrounding the enclosure44. The direction of refrigerant flow is indicated by arrows in FIG. 2.

The compressor unit 14 may comprise one or more sensors (notillustrated) for determining the state thereof during operation of thesystem 10. The outputs of these sensors may be used by the controller 40to determine how to control operation of the compressor unit 14, as willbe explained below.

The compressor unit may be provided with one or more solar-sensitivemodules configured to measure the degree (i.e., intensity, etc.) ofsolar radiation which is available to or impinging upon the solarcollector 32. This may be accomplished by any desired means, for exampleby providing photovoltaic cells. The solar-sensitive modules may beconfigured for detecting and distinguishing between differentfrequencies of solar radiation, in particular infrared radiation. Thesolar-sensitive modules may be disposed adjacent the solar collector 32,or behind the enclosure 44 thereof. The controller may determine theamount of solar energy which is available for contributed to the systembased on the degree of solar radiation measured by the solar-sensitivemodules. For example, the solar radiation measured may be multiplied bya factor equal to the amount by which the area of the solar coil 42exceeds the total area of photo-sensitive material in the modules.

In addition to or alternatively to the above, temperature and/orpressure sensors may be disposed at the entrance to and exits from thesolar coil 42. The controller 40 may use the temperatures and/orpressures measured at these points during operation of the system 10,together with other factors, such as type of refrigerant, etc., todetermine the amount of the contribution of solar energy during use. Thecontroller 40 may be configured for using these measurements togetherwith those of the solar-sensitive modules, e.g., for performingreal-time verifications of the results of each set of measurements.

In addition, other sensors may be provided for measuring usageparameters of the compressor unit 14 and or the entire air-conditioningsystem. These sensors may be provided for any desired use, for examplefor feedback control to the various elements of the system.

As mentioned, the compressor unit 14 is designed to increase thepressure and temperature of gaseous refrigerant passing therethrough. Inuse, the controller determines the desired pressure/temperature at whichthe refrigerant should exit the compressor unit 14, for example based onthe cooling demand. It thus determines the contribution of solar energywhich will be provided via the solar collector 32. Once this has beendetermined, the controller 40 operates the mechanical compressor 30 toprovide the additional energy required to meet the cooling demand.

For example, if the motor 34 of the mechanical compressor 30 is providedwith a variable-speed drive, it may cause the motor to operate at ahighly reduced speed compared to that which would be necessary to meetthe cooling load in the absence of the solar collector 32. In theabsence of any sunlight, the compressor may operate as usual.

The condenser unit 16 may be designed similar to condenser units whichare typically provided for use in air-conditioning systems. As such, itcomprises a condenser coil 48, disposed so as to be in fluidcommunication with the refrigerant line 20, and a fan 50, or othersimilar forced air mechanism, designed to force air over the condensercoil. The condenser unit 16 is designed such that refrigerant whichenters the condenser coil 48 at an entrance 52 thereof in a gaseousstate exits the condenser coil at an exit 54 thereof in a liquid state.

The metering device 18 may be designed similar to metering devices whichare typically provided for use in air-conditioning systems. It may beprovided as a thermal (or thermostatic) expansion valve, which isdesigned to control the amount of refrigerant that flows from thecondenser unit 16 to the evaporator unit 12. In addition, the pressureof the refrigerant drops as it traverses the metering device 18, whichcontributes to increased efficiency of the air-conditioning system 10.

As illustrated in FIG. 3, the air-conditioning system 10 described abovemay be used as a heat pump, such that refrigerant is provided to theevaporator unit 12 at a temperature which is higher than that of thespace to be heated. Thus, when ambient is forced over it, it is heated.In order to operate thusly, the direction of flow needs to be reversed,except that it must pass through the mechanical compressor 30, andoptionally the compressor unit 14, in the same direction as duringcooling. For such a use, a reversing valve 56 is provided. The reversingvalve 56 may be designed similar to reversing valves which are typicallyprovided for use in air-conditioning systems.

Alternatively, as illustrated in FIG. 4A, the reversing valve 56 maycomprise two separate three-way valves: an inlet valve 58, which servesas an inlet to the compressor unit 14, and an outlet valve 60, whichserves as an outlet to the compressor unit. Each of the inlet and outletvalve 58, 60 comprises three ports (an evaporator-side port 58a, 60a,each connected to the evaporator unit 12 via a first supply connectionA; a condenser-side port 58b, 60b, each connected to the condenser unit16 via a second supply connection B, and a compressor-side port 58c,60c, connected, respectively, to the inlet of the mechanical compressor30 via C and the outlet of the solar unit 32 via D), two of which may bebrought into fluid communication with each other, while the third actsas a stopper.

During use to provide cooling via the evaporator unit 12, as illustratedin FIG. 4B, the inlet valve 58 is positioned such that theevaporator-side port 58a and compressor-side port 58c thereof are influid communication with each other, and the outlet valve 60 ispositioned such that the condenser-side port 60b and the compressor-sideport 60c thereof are in fluid communication with each other. Thecondenser-side port 58b of the inlet valve 58 and the evaporator-sideport 60a of the outlet valve 60 act as stoppers. Refrigerant from theevaporator unit 12 flows via the first supply connection A through theevaporator-side port 58a of the inlet valve 58, and exits via thecompressor-side port 58c thereof, from where it enters the mechanicalcompressor 30. Refrigerant from the solar collector 32 flows through thecompressor-side port 60c of the outlet valve 60, and exits via thesecond supply connection B through the condenser-side port 60b thereof,from where it enters the condenser unit 16. The direction of refrigerantflow is indicated in FIG. 4B by arrows.

During use to provide heating via the evaporator unit 12, as illustratedin FIG. 4C, the inlet valve 58 is positioned such that thecondenser-side port 58b and compressor-side port 58c thereof are influid communication with each other, and the outlet valve 60 ispositioned such that the evaporator-side port 60a and thecompressor-side port 60c thereof are in fluid communication with eachother. The evaporator-side port 58a of the inlet valve 58 and thecondenser-side port 60b of the outlet valve 60 act as stoppers.Refrigerant from the condenser unit 16 flows via the second supplyconnection B through the condenser-side port 58b of the inlet valve 58,and exits via the compressor-side port 58c thereof, from where it entersthe mechanical compressor 30. Refrigerant from the solar collector 32flows through the compressor-side port 60c of the outlet valve 60, andexits via the first supply connection A through the evaporator-side port60a thereof, from where it enters the condenser unit 16. The directionof refrigerant flow is indicated in FIG. 4C by arrows.

It will be appreciated that although the reversing valve 56 is describedas being positioned between the evaporator unit 12 and compressor unit14 on a first side, and the compressor unit and condenser unit 16 on asecond side (ensuring that refrigerant flow across the compressor unitis the same for all types of operations), it may be positioned betweenthe mechanical compressor 30 and solar unit 32 on the second side (onlyensuring that refrigerant flow across the mechanical compressor is thesame for all types of operations), such that refrigerant is heated bysolar radiation before being mechanically compressed.

The inlet and outlet valves 58, 60 may be mechanically coupled to oneanother in order ensure that they alter their states of fluidconnectivity (i.e., which ports are in fluid communication) in tandem,so as to prevent a situation where they are each positioned to operatein a different mode, which could lead to undesired performance of theair-conditioning system 10 and/or damage to components thereof.

According to a modification, as illustrated in FIG. 5, the compressorunit 14 may comprise upstream and downstream solar collectors 32a, 32b.Bypass lines 33a, 33b are provided, each being associated with one ofthe solar collectors 32a, 32b. Appropriate valves (e.g., three-wayvalves, non-return valves, etc.; not illustrated) are provided at endsof each of the bypass lines 33a, 33b in order to selectively routerefrigerant through the solar collector 32a, 32b or bypassing it. Thecontroller 40 is configured to operate the valves in order to properlyroute the refrigerant.

In use to provide cooling via the evaporator unit 12, the valves of thebypass line 33a associated with the upstream solar collector 32a areoperative to route refrigerant through the upstream solar collector, andthe valves of the bypass line 33b associated with the downstream solarcollector 32b are operative to route refrigerant to bypass thedownstream solar collector. Thus, refrigerant is only heated before itenters the compressor.

When there is no sunlight impinging on the upstream solar collector 32a,or if the measured temperature thereof is lower than that of therefrigerant, the valves may be operative to route refrigerant throughthe bypass line 33a associated with the upstream solar collector, suchthat the compressor unit 14 operates as a regular compressor.

In use to provide heating via the evaporator unit 12, the valves of thebypass line 33a associated with the upstream solar collector 32a areoperative to route refrigerant to bypass the upstream solar collector,and the valves of the both bypass lines 33a, 33b are operative to routerefrigerant through their respective solar collectors 32a, 32b. Thus,refrigerant is heated before it enters the compressor, and again once itleaves.

When there is no sunlight impinging on the solar collectors 32a, 32b, orif the measured temperature thereof is lower than that of therefrigerant, the valves may be operative to route refrigerant throughthe bypass lines 33a, 33b, such that the compressor unit 14 operates asa regular compressor.

According to another modification, as illustrated in FIG. 6, thecondenser unit 16 may comprise a heat exchanger 70 connected to a sourceof water. (It will be appreciated that although the heat exchanger 70 isrepresented in FIG. 6 with the symbol for a shell and tube heatexchanger, any appropriate heat exchanger may be provided.) Thus, theair-conditioning system 10, and specifically the condenser unit 16, mayserve as a part of a water heating system.

The solar collector 32 may comprise an arrangement designed forincreasing absorption of heat from solar radiation impinging on thesolar collector 32 and transferring it to the solar coil 42. Forexample, it may comprise a fin-tube arrangement, wherein the solar coil42 constitutes the tube thereof.

Alternatively, as illustrated in FIGS. 7A and 7B, it may comprise aheat-sink 62, for example made of extruded aluminum. The portions of thesolar coil 42 passing through the heat-sink 62 may be disposed withintubes 64 formed within the heat-sink, or the tubes 64 may constitutethose portions of the solar coil (i.e., the solar collector 32 may bedesigned such that refrigerant passes directly through the heat-sink,and is directed to an adjacent tube by a semi-circular coil 66 attachedto the end of each tube. Projections 68 are provided to increase thearea for impingement of incident solar radiation.

The surface of the heat-sink 62 may be designed to lower itsreflectivity. For example, it may be painted a dark color, coated with alow- or non-reflective materiel such as matte paint, etc.

Although one embodiment of the heat-sink 62 has been illustrated, itwill be appreciated that any appropriate shape which is configured forincreasing absorption of heat from solar radiation impinging on thesolar collector 32 and transferring it to the solar coil 42 may beprovided. For example, the heat-sink 62 may be provided as a flat slabof appropriate material with through-going bores constituting (or allowpassage therethrough of) portions of the solar coil 42.

It will be appreciated that although the above has been described inconnection with a solar collector, any thermal collector may besubstituted therefore without departing from the spirit and scope of thepresent invention, mutatis mutandis. For example, the air-conditioningsystem may be adapted for automotive use, with the thermal collectorbeing configured for capturing and utilizing waste heat from theoperation of the automobile for increasing the temperature of therefrigerant. Appropriate sensors may optionally be provided fordetermining the amount of thermal energy thus contributed, or expectedto be thus contributed. Other examples include thermal collectors whichare configured for capturing and utilizing waste heat from industrialapplications, including, but not limited to, ovens, laundry dryers, etc.

Those skilled in the art to which this invention pertains will readilyappreciate that numerous changes, variations and modifications can bemade without departing from the scope to of the invention mutatismutandis.

The invention claimed is:
 1. A temperature control system, the systemcomprising a closed refrigerant circuit, comprising: an evaporator unitconfigured for absorbing heat via the refrigerant, thereby evaporatingit the refrigerant; a compressor unit comprising: a mechanicalcompressor configured for increasing the pressure of the refrigerantwithin the circuit, and a thermal collector configured for utilizing anexternal heat source to increase the temperature of the refrigerantwithin the circuit; and a condenser unit configured for rejecting heatfrom the refrigerant within the circuit, thereby liquefying it therefrigerant, said condenser unit being the first unit downstream thethermal collector that rejects heat from the refrigerant.
 2. Thetemperature control system according to claim 1, wherein said thermalcollector comprises a solar collector configured for capturing heat fromincident solar radiation.
 3. The temperature control system according toclaim 2, wherein said solar collector comprises a refrigerant-carryingconduit within an evacuated enclosure, a radiation-facing side of theenclosure comprising a transparent material.
 4. The temperature controlsystem according to claim 3, wherein said enclosure is evacuated.
 5. Thetemperature control system according to claim 3, wherein said solarcollector further comprises a heat-sink associated with saidrefrigerant-carrying conduit, said heat-sink being configured to absorbsolar energy and transfer it to said refrigerant-carrying conduit. 6.The temperature control system according to claim 5, wherein saidheat-sink is formed with projections extending radially from saidrefrigerant-carrying conduit.
 7. The temperature control systemaccording to claim 5, wherein said heat-sink is made of an extrudedmaterial.
 8. The temperature control system according to claim 5,wherein said heat-sink is made of a metal.
 9. The temperature controlsystem according to claim 5, wherein at least radiation-facing surfacesof said heat-sink are designed to lower reflectivity thereof.
 10. Thetemperature control system according to claim 1 18, further comprising:temperature sensors disposed to measure the temperature of therefrigerant upon entering and exiting said thermal collector; and athecontroller configured to determine an expected temperature increase ofthe refrigerant in the thermal collector based on the temperaturemeasured by said temperature sensors, and to control operation of saidmechanical compressor by causing the variable-frequency drive to varythe speed of the mechanical compressor at least based on said expectedtemperature increase temperature of the refrigerant measured by thetemperature sensors.
 11. The temperature control system according toclaim 10, wherein said compressor unit comprises a variable-frequencydrive to vary the speed of the mechanical compressor.
 12. Thetemperature control unit according to claim 1, configured to operate avapor-compression refrigeration cycle.
 13. The temperature controlsystem according to claim 1, further comprising a metering devicedownstream of said condenser unit configured for regulating flow ofliquid refrigerant.
 14. The temperature control system according toclaim 1, being a split-system air conditioning system.
 15. Thetemperature control system according to claim 1, further comprising areversing valve configured to cause said refrigerant to flow in areverse direction, thereby enabling said evaporator unit to reject heatfrom the refrigerant, and said condenser unit to absorb heat to therefrigerant.
 16. The temperature control system according to claim 1,wherein said condenser unit constitutes a portion of a water heatingsystem, water heater being configured to utilize the heat rejected fromthe refrigerant to heat water.
 17. A temperature control system, thesystem comprising a closed refrigerant circuit comprising: an evaporatorunit configured for absorbing heat via the refrigerant, therebyevaporating the refrigerant; a compressor unit comprising: a mechanicalcompressor configured for increasing the pressure of the refrigerantwithin the circuit, a thermal collector arranged downstream of themechanical compressor, the thermal collector being configured forutilizing an external heat source to increase the temperature of therefrigerant within the circuit; a condenser unit configured forrejecting heat from the refrigerant within the circuit, therebyliquefying the refrigerant; and a reversing valve configured to causesaid refrigerant to flow in a reverse direction, thereby enabling saidevaporator unit to reject heat from the refrigerant and said condenserunit to absorb heat to the refrigerant, wherein the reversing valve isconfigured to maintain the thermal collector downstream of themechanical compressor when the refrigerant is caused to flow in saidreverse direction.
 18. The temperature control system according to claim1, the temperature control system being configured to meet a coolingload, wherein the mechanical compressor comprises a variable-frequencydrive configured to vary speed of the mechanical compressor, the closedrefrigerant circuit further comprising: a controller configured tocontrol operation of the mechanical compressor at least by causing thevariable-frequency drive to vary the speed of the mechanical compressor,wherein the system is configured to operate the mechanical compressor ata variable speed based on the cooling load and the temperature of therefrigerant.
 19. The temperature control system according to claim 17,the temperature control system being configured to meet a cooling load,wherein the mechanical compressor comprises a variable-frequency driveconfigured to vary speed of the mechanical compressor, and wherein thesystem is configured to operate the mechanical compressor at a variablespeed based on the cooling load and the temperature of the refrigerant.